F5 FirePass Content Inspection Management XSS

The F5 FirePass SSL VPN appliance provides rudimentary web request sanitization for resources exposed through the appliance via Portal Access. This Content Inspection feature can be configured and customized through the web management interface to optimize protection against cross-site scripting and SQL injection. The "XSS scripting" configuration page even prominently states the following:

"The FirePass can aid in preventing Cross Site Scripting attacks via vulnerable web servers. This is done by scanning URL arguments and form POST data sent by users through Web Applications, and blocking the request if it looks suspicious. Note that the FirePass user and admin console interfaces are already protected against Cross Site Scripting attacks."

Ironically these very pages contain cross-site scripting vulnerabilities. Specifically, parameter css_exceptions in page /vdesk/admincon/webyfiers.php and parameter sql_matchscope in page /vdesk/admincon/index.php are vulnerable due to incorrect handling of quotes. This allows an attacker to force premature termination of the parameter value and to inject an event handler script. This injection is permanent because it is embedded in the parameter value. At the same time it is possible to remove (also permanently) the "Update" button on the web form, which complicates the injection removal.